1. Field of the Invention
The present invention relates to an impact absorbing type steering column apparatus for a vehicle in which the impact energy absorption amount can be minutely controlled in the course of a collapse stroke upon secondary collision.
2. Background Art
When a vehicle collides with a building structure or the like, the driver sometimes suffers secondary collision with the steering wheel due to inertia. In order to protect drivers from such secondary collision, it has become a common practice to use an impact absorbing type steering column.
The impact absorbing type steering column apparatus has such a structure that when the driver suffers secondary collision and the impact energy acts on the steering column in the frontward direction of the vehicle, the steering column collapses to be detached from the vehicle body and moves forward (in a stroke), so that the impact energy is absorbed in the course of the collapse stroke.
For example, in a ripping type impact absorbing mechanism disclosed in Japanese Utility Model Application Laid-Open No. 5-68776, the central portion of an energy absorbing member in the form of a strip-shaped steel plate is fixed to a bracket on the vehicle body and both the end portions of the steel plate are bent in a U-shape and fixed to the steering column, so that when the steering column moves in the frontward direction of the vehicle, the energy absorbing member is deformed to be bent and ripped.
On the other hand, there is a drawing type impact energy absorbing mechanism in which an end of a metal wire is fixed to a bracket on the steering column and the wire is wound around a tilt bolt on the vehicle body and extended toward the front side of the vehicle. Thus, when the steering column moves in the frontward direction of the vehicle, the wire is drawn and deformed by the tilt bolt.
However, the above-described impact absorbing type steering column apparatuses for a vehicle are designed in such a way that substantially constant impact energy is absorbed as the collapse stroke progresses. Therefore, it is not possible to control the impact energy absorption amount in the course of the collapse stroke or in accordance with the type of the vehicle.